Integrated optical structures with electrically conductive parts

ABSTRACT

The invention concerns a integrated optical structure comprising a plurality of parts made at least of a dielectric material, stacked according to the levels of integration and defining at least an optical microguide, and further comprising at least an integrated part ( 15 ) made of an electrically conductive material, interposed or inserted between at least two of said dielectric parts and having at least one part ( 11   a ) externally accessible to said dielectric parts for at least an external electrical connection.

The present invention relates to the field of integrated opticalstructures.

In general, an integrated optical structure comprises a multiplicity ofparts made of dielectrics, these being stacked in levels of integrationand defining integrated optical microguides for the transmission,conversion or treatment of light waves.

Certain integrated optical structures furthermore have metallic surfaceregions that are connected via metal wires, constituting wire bridges,to an electrical control or supply source. This is in particular thecase in integrated optical structures that include actuators composed ofcombs lying in a cavity and having tines lying along and at a certaindistance from fixed surfaces, said metallic regions extending along thelateral faces of the tines and along the fixed surfaces so as toconstitute comb displacement electrodes.

Such arrangements have the following main drawbacks. The operations ofmounting the electrical connection wires are time-consuming and tedious,and must be carried out accurately. These electrical connection wiresproject from the surface of the optical structures and there is a riskof them touching one another.

The object of the present invention is to improve integrated opticalstructures so as to facilitate and improve the electrical connections offunctional parts of such structures that require a power supply.

The integrated optical structure according to the invention comprises amultiplicity of parts made of at least one dielectric, that are stackedin levels of integration and define at least one optical microguide.

According to the invention, this structure furthermore includes at leastone conducting integrated part made of an electrically conductingmaterial, that is interposed or inserted between at least two of saiddielectric parts, and at least one connection part made of anelectrically conducting material, externally accessible to saiddielectric parts for the purpose of making at least one externalelectrical connection to this conducting integrated part.

The integrated structure according to the invention comprises at leasttwo groups of electrically conducting regions produced in one level ofintegration.

According to the invention, at least one conducting integrated partincludes at least one main part lying in a different level ofintegration from that of said groups and crossing at least oneconducting region of one of said groups and secondary parts lyingperpendicular to the planes of integration and connecting this main partand the conducting regions of the other group.

According to the invention, at least two conducting integrated parts mayadvantageously comprise at least one main part lying in at least onelevel of integration and secondary parts, respectively, which connecttheir main parts and the metal regions of said groups, respectively.

According to the invention, at least one of said upper conductingregions preferably includes at least one part constituting an electrode.

The integrated structure according to the invention may advantageouslyinclude a moveable member provided with at least one electrode locatedopposite, and at a certain distance from and electrically coupled to,said part, constituting an electrode so as to form an optical actuator.

According to the invention, said moveable member may advantageouslycarry at least one optical microguide.

According to the invention, at least one conducting integrated partpreferably includes at least one main part lying in one level ofintegration and, at least at one point in this main part, a secondarypart lying perpendicular to the planes of integration and passingthrough at least one dielectric part adjacent to this point.

According to the invention, at least one secondary part preferablyconstitutes an external electrical connection part.

According to the invention, at least two conducting integrated partspreferably include main parts lying in different levels of integration.

According to the invention, said conducting integrated parts preferablyinclude main parts that intersect at a point and at least one secondarypart lying perpendicular to the planes of integration and passingthrough the dielectric part or parts separating said main parts at thispoint so as to connect these main parts.

According to the invention, at least one conducting integrated partpreferably includes at least one integrated main part constituting anelectrical resistor lying along and in the vicinity of one part of anintegrated microguide and secondary parts that are externallyaccessible, for the purpose of making an external electrical connectionto this main part.

According to the invention, said electrical resistor is preferably aresistance heating element.

According to the invention, said electrical resistor may advantageouslybe a temperature measurement resistor.

According to another embodiment of the invention, at least oneconducting integrated part may advantageously include at least oneintegrated main part constituting an electrical resistor lying along andin the vicinity of one part of an integrated microguide and secondaryparts that are externally accessible, for the purpose of making anexternal electrical connection to this main part.

According to the invention, said electrical resistor may be a resistanceheating element.

According to the invention, said electrical resistor may be atemperature measurement resistor.

The present invention will be more clearly understood on examiningintegrated optical structures that are described by way of non-limitingexamples and illustrated by the drawing in which:

FIGS. 1 to 6 show, in section, an integrated optical structure accordingto the present invention, in its successive fabrication steps;

FIG. 7 shows a top view of another integrated optical structureaccording to the present invention;

FIG. 8 shows a cross section on VIII-VIII of the integrated opticalstructure of FIG. 7;

FIG. 9 shows a cross section on IX-IX of the integrated opticalstructure of FIG. 7;

FIG. 10 shows a cross section on X-X of the integrated optical structureof FIG. 7;

FIG. 11 shows a cross section of another integrated optical structureaccording to the present invention;

FIG. 12 shows a horizontal section on XII-XII of the integrated opticalstructure of FIG. 11; and

FIG. 13 shows, in section, an alternative embodiment of the integratedoptical structure of FIGS. 1 to 6.

FIG. 1 shows an integrated optical structure 1 in the course offabrication, which comprises a support wafer 2, for example made ofsilicon, on one face of which a layer 3 made of a dielectric orelectrically nonconducting material, for example undoped silica, isdeposited.

Next, a layer 4 made of an electrically conducting material, for examplepolycrystalline silicon, titanium, titanium nitride or tungsten, isdeposited. Depending on predetermined requirements, one or moreconducting tracks or regions 5 are then produced, using aphotolithography and etching process, by removing the material of thelayer external to these regions 5.

FIG. 2 shows how the process continues with the deposition of a layer 6of a dielectric or electrically nonconducting material, for exampledoped silica, silicon nitride or silicon oxynitride. The layer 6 is suchthat the conducting tracks or regions 5 produced above are covered.

After optional planarization of the surface of the layer 6, a layer 7made of an electrically conducting material, for example polycrystallinesilicon, titanium, titanium nitride or tungsten, is deposited.

One or more conducting tracks or regions 8 are then produced using aphotolithography and etching process, by removal of the material of thelayer 7 external to these regions 8.

Referring to FIG. 3, an optical wave transmission core 9 a of square orrectangular cross section is then produced in the dielectric layer 6using a photolithography and etching process, by removal of the materialof this layer 6 on either side of this core, this operation beingcarried out in such a way that the transmission core 9 a has apredetermined design or path.

Of course, during the design of the optical structure 1, thenonconducting tracks or regions 5 and 8 are preferably arranged so as tobe located laterally to and at a certain distance from the transmissioncore 9 a to be obtained.

Next, as shown in FIG. 4, a layer 10 of a dielectric or electricallynonconducting material, for example undoped silica, is deposited. Thislayer 10 fills the spaces left on either side of the transmission core 9a produced in the layer 6 and covers the conducting regions or tracks 8.

As a result, the transmission core 9 a and the layers 3 and 10 thatsurround it define an integrated optical microguide 9.

Next, as shown in FIG. 5, holes or wells 11, passing through thedielectric layers 6 and 10 and emerging at points located above theconducting tracks or regions 5, and holes or wells 12, passing throughthe layer 10 and emerging at points located above the conducting regionsor tracks 8, are produced, for example using a photolithography andetching process.

Finally, as shown in FIG. 6, a layer 13 made of an electricallyconducting material, for example polycrystalline silicon, titanium,titanium nitride, tungsten or aluminum, is deposited, this materialfilling the holes or wells 11 and 12 so as to constitute interconnectvias 11 a and 12 a.

Next, using a photolithography and etching process, upper conductingregions 14 are produced by removal of the material of the layer 13external to these regions, these conducting regions 14 lyingrespectively above at least one of the holes or wells 11 and 12 producedbeforehand and filled by the interconnect vias 11 a and 12 a.

As a result of the foregoing operations, the integrated opticalstructure 1, as shown in definitive form in FIG. 6, compriseselectrically conducting integrated parts 15 that have main partsconsisting of the conducting tracks or regions 5 produced in the planeof integration subjacent to the transmission core 9 a and secondaryparts consisting of the interconnect vias 11 a formed perpendicularly tothis plane of integration, respectively, and electrically conductingintegrated parts 16 that have main parts consisting of the conductingtracks or regions 8 produced in the plane of integration subjacent tothe upper layer 10 and secondary parts consisting of the interconnectvias 12 a formed perpendicular to this plane of integration,respectively.

The interconnect vias 11 a and 12 a are accessible externally to thestructure 1, the upper conducting regions being produced so as to makeit easier for external electrical connections to the integratedconducting parts 15 and 16 and/or so as to produce, according topredetermined requirements, selective electrical interconnects betweenthese integrated conducting parts.

In the example shown in FIG. 6, the integrated optical structure 1 issuch that the conducting integrated parts 15 and 16 are placed asufficient distance from the transmission core 9 a of the opticalmicroguide 9 so as not to disturb the propagation of the optical wave inthis transmission core 9 a.

In an alternative embodiment, the conducting regions or tracks 5 and 7could be formed in trenches provided in the dielectric layers 3 and 6after chemical-mechanical polishing of the conducting layers 4 and 7that fill these trenches.

Referring to FIGS. 7 to 10, an integrated optical structure 100 will nowbe described that implements in one particular way the arrangementsdescribed with reference to FIGS. 1 to 6.

The optical structure 100 comprises, as in the previous example, asupport wafer 101 corresponding to the support wafer 2 and, insuccession, three layers 102, 103 and 104 corresponding to the layers 3,6 and 10.

The structure 100 has a cavity 105 hollowed out through the layers 102,103 and 104 and into the support wafer 101, said cavity having twoparallel walls 105 a and 105 b, an end wall 105 c and a bottom 105 d.

The cavity 105 is produced so as to form an actuator 106 that comprisesa moveable member 107 free underneath and having a main branch 108, thatextends parallel to the walls 105 a and 105 b, and, on each side of thismain branch 108, spaced-apart transverse secondary branches 109 and 110,and also fixed parts 111 and 112 that project from the walls 105 a and105 b, and the sidewalls or lateral faces of which lie parallel to and acertain distance from the sidewalls or lateral faces of the secondarybranches 109 of the moveable member 107.

The upper face of the moveable member 107 and the sidewalls or lateralfaces of its secondary branches 109 and 110 are covered with a coatingof an electrically conducting material 113 so as to constituteelectrodes.

The opposed sidewalls or lateral faces of the fixed parts 111 and 112and the upper face of these projecting parts 111 and 112 are providedwith coatings 114 and 115 made of an electrically conducting materialrespectively, these being electrically isolated from each other so as toconstitute independent electrodes. These coatings 114 and 115 extendbeyond the projecting parts 111 and 112 on the upper face of the layer104 so as to constitute independent electrically conducting upperregions 116 and 117.

The upper face of the layer 104 furthermore carries coatings 118 and 119made of a conducting material which run along at a certain distance fromthe end wall 105 c of the cavity 105.

The optical structure 10 includes, on either side of and at a certaindistance from the cavity 105, the integrated conducting parts 120 and121 that correspond to the integrated conducting parts 15 and 16 of theexample described with reference to FIG. 6.

As shown in FIG. 9, the integrated conducting parts 120 compriseintegrated main parts or tracks 122 and interconnect vias 123 that areformed below the upper conducting regions 116 and the upper conductingregion 118, respectively. Thus, all the corresponding electrodes 114 areelectrically connected together.

Likewise, as shown in FIG. 10, the integrated conducting parts 121comprise integrated main parts or tracks 124 and interconnect vias 125that are formed below the upper conducting regions 116 and the upperconducting region 118, respectively. Thus, all the correspondingelectrodes 115 are electrically connected together.

It is then possible to connect all the electrodes 114 and all theelectrodes 115 to a power supply solely by two electrically conductingwires 126 and 127 that are soldered to one of the upper conductingregions 116 and 117 or to the upper conducting regions 118 and 119,respectively.

By supplying power to the electrodes 113 of the moveable member 107 viaelectrical connection means (not shown) such as an electrical wire andby supplying power selectively to the electrodes 113, by means of theelectrical wires 127 and 128, the moveable member 107 of the actuator106 can be displaced parallel to its main branch 108 in one direction orthe other.

In one example, the moveable member 107 of the actuator 106 may beconnected to a beam or to an optical switching platform carrying one ormore optical microguides as described in patents FR-A-90/03902 andFR-A-95/00201.

FIGS. 11 and 12 show an integrated optical structure 200 that comprisesa Mach-Zehnder interferometer 201 formed by an input microguide 202, anoutput microguide 203 and two microguides 204 and 205 that connect themicroguides 202 and 203 in parallel.

The optical structure 200 furthermore includes an electricallyconducting integrated part 206 produced like the integrated conductingpart 15 described with reference to FIG. 6.

This integrated conducting part 206 comprises a main part 207, that isproduced in the plane of integration of the aforementioned opticalmicroguides and lies along and a short distance from the opticalmicroguide 205, and two interconnect vias 208 and 209 for electricallyconnecting the ends of the conducting main part 207 to an external powersupply.

The main part 207 of the integrated conducting part 206 may then form aresistance heating element capable of varying, by thermal conduction,the temperature of the optical microguide 205 in such a way that theMach-Zehnder interferometer 201 can form an optical switch, an opticalattenuator or an optical interrupter.

According to another embodiment, the main part 207 of the integratedconducting part 206 could be used for the purpose of measuring thetemperature of the structure in its environment.

FIG. 13 shows an integrated optical structure 300 that differs from theintegrated optical structure 1 described with reference to FIGS. 1 to 6by the fact that, before the conducting layer 7 is deposited on thedielectric layer 6 at least one hole 301 is made in this dielectriclayer 6 above at least one conducting track or region 5.

As the conducting layer 7 is being deposited, the material of which itis composed fills the hole 301 and constitutes an interconnect via 301a.

During the step of etching the conducting layer 7, a track or region 8is produced above the hole 301 and is electrically connected to thetrack or region 5 beneath the interconnect via 301 a.

Thus, electrical connections between levels may be produced.

The present invention is not limited to the examples described above.Many alternative embodiments are possible without departing from thescope defined by the appended claims.

1. An integrated optical structure (100), comprising: a support wafer(101); in succession, three dielectric layers (102, 103, 104) located onsaid support wafer; a cavity (105) hollowed out through the threedielectric layers and into the support wafer, said cavity having twoparallel walls (105 a, 105 b), an end wall (105 c) and a bottom (105 d);an actuator (106) located within said cavity and comprising a moveablemember (107) having i) a main branch (108) that extends parallel to saidparallel walls (105 a, 105 b), ii) spaced-apart transverse secondarybranches (109, 110) connected to said main branch, each second branchhaving a free lower surface spaced apart from said bottom of said cavitywith a free space between the lower surface and said bottom of saidcavity, and iii) fixed parts (111, 112) projecting from said twoparallel walls (105 a, 105 b) and respectively extending between saidtransverse secondary branches so that sidewalls of said fixed parts lieparallel to sidewalls of said secondary branches, first electrodes (113)located on an upper surface of said transverse secondary branches,second electrodes (114, 115) located on an upper surface of said fixedparts; exactly and only two external upper conducting regions (118, 119)configured so that by supplying power to only said two upper conductingregions displaces the moveable member (107) of the actuator (106) withrespect to the main branch (108); and connections connecting said secondelectrodes to said two external upper conducting regions, saidconnections including tracks (122, 124) located between said dielectriclayers and plural vias (123, 125) that run up from the tracks to theupper conducting regions and the second electrodes.
 2. The integratedoptical structure (100) of claim 1, wherein, said first electrodesfurther cover the sidewalls of said transverse secondary branches, andsaid lower surface free of said transverse secondary branches is free ofsaid first electrodes.
 3. The integrated optical structure (100) ofclaim 2, wherein, said second electrodes further cover the sidewalls ofsaid fixed parts, the second electrode of each fixed part beingelectrically isolated from the other second electrodes so that eachsecond electrode constitutes an independent electrode.
 4. The integratedoptical structure (100) of claim 3, wherein, the secondary electrodesextend beyond the fixed parts and onto an upper face of an uppermost one(104) of the three dielectric layers, and further comprising independentelectrically conducting upper regions (116, 117), located on the upperface of the uppermost dielectric layer, terminating each of thesecondary electrodes.
 5. The integrated optical structure (100) of claim1, wherein, said two external upper conducting regions compriseconductive coatings (118, 119) running on an upper face of an uppermostone (104) of the three dielectric layers at a distance spaced from theend wall (105 c) of the cavity (105).
 6. The integrated opticalstructure (100) of claim 1, wherein, said connections connecting saidsecond electrodes to said two external upper conducting regions areintegrated conducting parts (120, 121) comprising the tracks (122, 124)running between two of said three dielectric layers and interconnectingthe vias (123) running up through at least one of said three dielectriclayers.
 7. The integrated optical structure (100) of claim 6, whereinsaid integrated conducting parts are all formed below an uppermostsurface of an uppermost one of said three dielectric layers.
 8. Anintegrated optical structure (100), comprising: a support wafer (101);plural dielectric layers (102, 103, 104) located one on another on saidsupport wafer; a cavity (105) hollowed out through the dielectric layersand into the support wafer, said cavity having two parallel walls (105a, 105 b), an end wall (105 c) and a bottom (105 d); an actuator (106)located within said cavity and comprising a moveable member (107) havingi) a main branch (108), ii) spaced-apart transverse secondary branches(109, 110) connected to said main branch, each second branch having afree lower surface spaced apart from said bottom of said cavity, andiii) fixed parts (111, 112) projecting from said two parallel walls (105a, 105 b) and respectively extending between said transverse secondarybranches, first electrodes (113) located on an upper surface of saidtransverse secondary branches, second electrodes (114, 115) located onan upper surface of said fixed parts; two external upper conductingregions configured for connecting exactly two conducting wires to powersaid actuator so that the moveable member (107) of the actuator (106) isdisplaced with respect to the main branch (108); and connections locatedexclusively within the dielectric layers and connecting said secondelectrodes to said two external upper conducting regions, saidconnections including tracks (122, 124) located between said dielectriclayers and plural vias (123, 125) that run up from the tracks to theupper conducting regions and the second electrodes.
 9. The integratedoptical structure (100) of claim 8, wherein, said first electrodesfurther cover the sidewalls of said transverse secondary branches whileleaving said lower surface free of said transverse secondary branchesfree of said first electrodes, said second electrodes further cover thesidewalls of said fixed parts, the second electrode of each fixed partbeing electrically isolated from the other second electrodes so thateach second electrode constitutes an independent electrode, thesecondary electrodes extend beyond the fixed parts and onto an upperface of an uppermost one (104) of the dielectric layers.
 10. Theintegrated optical structure (100) of claim 8, wherein, said twoexternal upper conducting regions comprise conductive coatings (118,119) running on an upper face of an uppermost one (104) of thedielectric layers at a distance spaced from the end wall (105 c) of thecavity (105) and with a length greater than a corresponding length ofthe cavity.
 11. The integrated optical structure (100) of claim 8,wherein, said connections connecting said second electrodes to said twoexternal upper conducting regions are integrated conducting parts (120,121) comprising the tracks (122) running between two of said dielectriclayers and interconnecting the vias (123) running up through at leastone of said dielectric layers.
 12. An integrated optical structure(100), comprising: a cavity (105) located within a succession ofdielectric layers, said cavity having two parallel walls (105 a, 105 b),an end wall (105 c) and a bottom (105 d); an actuator 106 located withinsaid cavity and comprising a moveable member (107) having i) a mainbranch (108) that extends within said parallel walls (105 a, 105 b), ii)spaced-apart, transverse movable secondary branches (109, 110) connectedto said main branch, and iii) fixed parts (111, 112) projecting fromsaid two parallel walls (105 a, 105 b) and respectively extendingbetween said transverse secondary branches, first electrodes (113)located on said transverse secondary branches, second electrodes (114,115) located on said fixed parts; two external upper conducting regionsconfigured so that by supplying power to only said two external upperconducting regions displaces the moveable member (107) of the actuator(106) with respect to the main branch (108); and connections connectingsaid second electrodes to said two external upper conducting regions,said connections including tracks (122, 124) located between saiddielectric layers and plural vias (123, 125) that run up from the tracksto the upper conducting regions and the second electrodes.